Most auxiliary apparatuses of a motor vehicle engine—such as the alternator, the power steering pump and the air conditioner compressor shaft—are driven by a serpentine belt connected to a pulley on the crankshaft of an engine. The belt, in turn, drives pulleys on the auxiliary apparatuses.
It is well-known that the serpentine drive belt on a multi-cylinder engine seldom transmits constant torque to the various accessories which it drives. As the pistons sequentially fire, there are sudden torsional impact forces transmitted through the belt to the auxiliary apparatuses. A driven apparatus, such as an alternator, may have significant rotational inertia resisting changes to its rotational velocity, which can cause stress on the serpentine belt and other apparatuses in the belt system.
The prior art discloses the use of a one-way overrunning clutch for a driven pulley. The one-way clutch operates such that it only transmits torque in one rotational direction. However, while such a design allows an auxiliary apparatus to spin freely when the engine makes sudden negative changes in speed—such as when a down-shift occurs or when the engine is turned off—the use of a one-way clutch alone does not address the torsional impacts that occur due to the sequential firing of pistons in a multi-cylinder engine, or other reasons.
The prior art further discloses the use of devices within a pulley assembly to dampen or reduce the effect of harmful torsional impacts in a belt driven system. However, such prior art does not adequately address the situation described above, where a sudden reduction in the speed of the engine occurs. In such a situation, while the damping devices may absorb some of the torsional impact, the significant rotational inertia of an auxiliary apparatus, such as an alternator, will cause a tremendous amount of stress on the belt and on other engine accessories and apparatuses, potentially reducing the lives of such parts.
Further, the manner in which the devices in the prior art attempt to reduce the effect of harmful torsional impacts is not as effective as that disclosed in the present invention.